Print engines utilizing flexible belts rather than drums as a carrier for the engine's photoreceptor have been described in U.S. Pat. No. 4,652,115, issued to Palm et al. on Mar. 24, 1987 and assigned to the assignee of the present invention. In this flexible belt system, sequential images are formed on a photoreceptor belt and then transferred to an intermediate transfer belt in an overlapping fashion to form a final composite image on the final transfer belt. This composite image is then transferred to a final image receptor such as a sheet of paper. In the operation of this transfer belt, it is necessary to rotate the belt three entire revolutions for each three color composite image prior to a transfer to the final sheet of paper. Each revolution of the belt corresponds to a "plane" and for every three revolutions corresponding to a full composite image is referred to as a "page".
At the end of each page, i.e., for each three revolutions, it is necessary to remove any residual toner from the intermediate transfer belt prior to initiating the next page. This is not necessary with the systems that do not utilize the intermediate transfer belt since the receptor of the images that form the composite images is completely removed in the form of a sheet of paper. This is typical with drum systems. However, since the same transfer medium is utilized for subsequent copies, it is important that the surface characteristics of this medium be repeatable for each new page.
Typically, the surface of flexible belts has been "conditioned" or cleaned with the use of either a polishing roller or a cleaning blade. The polishing roller can be either a very fine brush or a very smooth surface which rotates in the opposite direction of travel of the belt with a predetermined velocity and a pressure. In comparison, a cleaning blade is disposed at a predetermined angle and pressure. By varying the parameters, the "aggressiveness" with which the cleaning member attacks the surface of the belt will be varied. The surface characteristics such as surface charge, etc. on the belt will be affected by these cleaning mechanisms. The present invention relates to the surface characteristics.
It has been noticed that subtle image defects occurred, which have been referred to as fine line break-up, for multiple copies. Although not entirely understood, this appears to be due to a change in the characteristics of the belt which are due to the toner, the application of electricity and to the general cleaning procedure. In connection with the flexible belt system utilizing an intermediate transfer belt, this problem is somewhat exacerbated in that the action of the cleaning mechanism must be interacted with the dynamics of the system. This is due to the fact that the cleaning system is only used at the end of each page when all three component images have been transferred to the intermediate transfer belt to form the composite images and the image transferred. The cleaning mechanism is then activated to clean off any residual toner and then the first component image for the next page transferred. The cleaning mechanism is then deactivated such that the cleaning operation is "page intermittent".
An important aspect of the cleaning mechanism with respect to the intermediate transfer belt is that the cleaning mechanism is activated at the end of one page for a part of the revolution of the transfer belt. However, while the cleaning mechanism is activated, transfer of at least the first one of the component images is being made. Therefore, it is important that the interaction between the cleaning mechanism and the registration of the belt be maintained. If any slippage occurs as a result of the cleaning operation and the interaction between the transfer belt and the cleaning mechanism, this could present problems. Therefore, registration provides some limitations to how much interaction the cleaning mechanism can have with the transfer belt. Although the cleaning mechanism of the present removes the unwanted toner, additional conditioning of the belt may be required in order to ensure that the characteristics of the belt are somewhat uniform; that is, conditioning is needed for the transfer belt.